So I've had an Arduino UNO for a year or so now, and everything works fine with the actual board. I lent it to an interested friend for a while and kept the same Arduino IDE on my Windows 10 PC. My friend used a Mac to mess with it, but I didn't think it would matter (I'm new to this; I never played with the Arduino much until today). He did the same basic projects on it that I did. Today I got it back, plugged it in, and the UNO turned on (no sensors attached). When I try to run the Blinking_LED program, I get this error message:
avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
Also, when I try to reset the COM port, I go to Tools, but the option "Port" is unhighlighted and will not let me click it. I've deleted and re-dowloaded the IDE to my PC but I'm still encountering the exact same problems. Any suggestions on how to resolve this would be GREATLY appreciated! :) P.S. If it makes any difference, the PC has no reaction to the UNO being plugged in.